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What Taylor says about a possible separating doublet or triplet is a
possibility, but it sounded from the first post more like this is a
solid opal that has simply lost its polish. The standard for
polishing opals is either 50 or 100K diamond on a poly pad or cerium
oxide on felt. I prefer the latter myself. Linde A is not necessary.
Also, opals do not 're-saturate'. Once the internal fluids have
dissapated, they will not take on moisture again. When ladies wear
their opals for doing dishes, they sometimes turn slightly to a
yellowish color on the surface but the internal structure remains
the same.
It is important to keep a good polish on opal as that produces a
glassy surface and reduces the possibility of 'crazing' and best
displays the internal 'fire'. In reality, virtually all opals will
craze or crack in time....some will do it early, others take years.
Because they are relatively soft, 5.5 to 6.5 on Mohs scale though
most around 5.5 to 6, opals will lose their polish fairly easily in
normal wear, especially if not protected. They are reasonably easy
to polish but this is often complicated when they remain in a
setting because it is impossible to get access to the entire
surface. Unless they are flush inlay, the best thing is to take the
stone out of the piece, smooth the entire surface on at least a 600
soft diamond wheel (such as Nova), prepolish on 1200 soft diamond
wheel and then polish on a felt pad with damp cerium oxide turning
at about 200RPM.
Be careful not to chip the stone with taking it out or resetting.
Opal is not only soft but very brittle.
Cheers from Don at The Charles Belle Studio in SOFL where simple
elegance IS fine jewelry! dcdietz AT comcast.net